Air Injection: Description and Operation

SECONDARY AIR INJECTION SYSTEM

The purpose of the Secondary Air Injection System (AIR) is to minimize hydrocarbon and carbon monoxide emissions during cold starts, and to speed the heating of the Three-Way Catalytic Converter (TWC). By supplying fresh air to the exhaust manifold when starting a cold engine, the AIR pump helps to afterburn unburned hydrocarbon. This makes it possible to increase injection time and retard ignition which give higher exhaust temperatures, speeding the activation of the TWC.





The AIR System Consists of:
^ AIR pump (1) which is activated via the AIR pump relay (2). The AIR pump is fitted with a filter and its inlet manifold is directed towards the side member to avoid taking in dirt and water. Pump and relay are protected by a 40 amp fuse located in the central electrical unit. A bimetal circuit breaker in the pump, which can be reset, opens if the system overheats.
^ Shut-off valve (3) which regulates the air supply to the exhaust manifold.
^ Solenoid (4) which controls the shut-off valve using under-pressure in the intake manifold.
^ Non-return valve (5) which prevents exhaust gases from returning to the pump when the system is not in operation.

The LH-control module controls the AIR pump relay and the solenoid which start the AIR pump and open the exhaust valve when the system is activated. Air travels from the pump to the exhaust manifold via the shut-off valve and the non-return valve.

If engine coolant temperature is between 10°C and 30°C (50°F - 85°F) and the car is running, then the auxiliary air system is activated 20 seconds after the engine is started. Once the system has been activated it runs for 45 to 120 seconds depending on the coolant temperature.